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Full text of "Programming"

Kinect Hacking: Weather Map 



J 



Make] Projects 



build, hack, tweak, share, discover.' 



Kinect Hacking: Weather Map 



Written By: Joshua Blake 



TOOLS: 



Compiler and IDE software (1) 
Microsoft Visual Studio 2010 Express 
(free) or other 2010 edition 

Computer (1) 

If you don't have Windows 7. you can 
still do everything described here with 
other Kinect drivers, but you'll need to 
translate the sample code into your own 
language and SDK of choice. 

Kinect development software (1) 
If you want to do additional development 
with the SDK or try out the audio 
features of Kinect. see the Kinect SDK 
Readme for additional software to install. 



PARTS: 

Kinect for Xbox 360 retail box (1) 
$150. includes the Kinect Sensor Power 
Supply that you'll need for plugging 
Kinect into your computer. The "Xbox 
Console with Kinect" bundles do not 
include this power supply, but if you've 
already got a bundle, you can buy the 
power supply separately for $35. 



SUMMARY 

Kinect for Xbox 360 is an amazing little device stuffed with magical sensors. Its 
revolutionary power and affordability ($150 without the Xbox console) has sparked a wave of 
innovation in human-computer interfaces that engage the whole body. Now all kinds of 
games and gadgets can recognize your movements and gestures as commands to do all 
kinds of things, without you having to wear anything. 

This article will explain what Kinect is, how it works, and how you can develop your own 
Kinect hacks. As a starter application, I'll explain the Kinect Weather Map, a live video 
application that changes your background to a different animated weather map whenever you 



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Kinect Hacking: Weather Map 

walk across the frame and turn — just like a TV meteorologist, but without a green screen. 

Step 1 — Kinect Hacking: Weather Map 



Infrared camera 
Color camera 
Infrared projector 




Microphone array 




• In terms of components, Kinect integrates several sensors: a color (RGB) camera and an 
infrared (IR) camera, each capable of 640x480 pixel resolution at 30 frames per second 
(fps), a microphone array that isolates speech from background noise, and a 3-axis 
accelerometer, which is used to detect whether Kinect is level. 

• Along with the sensors are a motor that tilts Kinect up and down, and a laser IR projector 
that uses a diffraction grating to project a speckle pattern onto the world in front of it. For 
power, Kinect requires 12V at 1 .08A, which means you either plug it in with a wall wart or 
you can splice it to battery power, like an 8xAA battery pack. 



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Kinect Hacking: Weather Map 



Step 2 — The Z-plane and the skeleton. 



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• The IR projector and IR camera are where the magic begins. Here's a simplified 
explanation. 

• Every small grouping of dots in the projected IR laser speckle pattern is unique and 
recognizable to the IR image processor, even when deformed or displaced against the rest 
of the pattern. The IR projector is physically offset from the IR camera, about 5" left of it 
from the camera's POV, which lets Kinect triangulate a depth value by determining the 
shift of each dot group. 

• Any point in the speckle pattern will shift rightward, as seen by the camera, as it reflects 
off of a closer surface — like the way your car's headlights' reflections diverge as you 
approach a reflective surface. 

• Image 1 shows an example of a horizontal slice representing dot brightness with numbers 
1-6. In one part of its view field, the camera would see 6-1-2-3-4 reflected from 1 meter 
away, and 2-3-4-5-6 reflected from 2m. Also note the darkened triangle, which shows the 
area that the IR camera sees that is in the shadow of the object as illuminated by the 
projector. Kinect can't determine depth data for these parts of the scene without 
interpolating, giving possibly inaccurate values. 

• Kinect generates a depth image from each dot pattern offset, and transmits it via USB 
cable to the Xbox 360 or PC. Each pixel in the depth image represents a distance away 
from the camera plane in millimeters. 

• In addition, on the XBox 360 and PC, advanced software performs the sophisticated task 
of recognizing humans from the depth image and identifying (x, y, z) positions for up to 20 
skeleton joints. The depth image and joints are available to developers, along with the RGB 
image from the color camera. These images are mirrored, so when you face a Kinect and 

a display, your left hand shows up on the left side of the image. 



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Kinect Hacking: Weather Map 

Step 3 — Kinect hacking setup. 

• Commercial Kinect games are written using the Xbox Development Kit, which is only 
available to game studios with Xbox publishing agreements. For the rest of us, the current 
best way to tap into Kinect is to write client applications for a Windows PC connected to 
Kinect via a USB cable. 

• To enable your PC to communicate with Kinect, you need to install a set of drivers and an 
SDK (software development kit) defining the structures you can call from your program to 
get the data. There are 3 options here: libfreenect and OpenNI, which were developed 
independently, and the Kinect for Windows SDK, which Microsoft officially released more 
recently. 

• For this article, I'm using Kinect for Windows SDK, which requires a PC running Windows 
7. (You can do everything described below with other Kinect drivers, but you'll need to 
translate the sample code into your own language and SDK of choice.) The Kinect SDK 
has a non-commercial use license during the beta, and a commercially licensed version is 
currently under development for release in early 2012. 

• If you already have libfreenect or OpenNI installed and you want to install the Kinect SDK, 
you must first plug in Kinect and un-install the previous drivers. To do this, open Windows 
Device Manager, right-click the Kinect Camera, Audio, and Motor devices, and then check 
the "Delete the driver software" checkbox, and confirm by clicking OK. Then launch Add or 
Remove Programs, and un-install any other driver installation packages listed that have 
Kinect in the name. 

• We'll write an application in 2 languages: XAML and C#. The visuals and controls are 
designed in XAML, a markup language for Windows interfaces that's based on the XML 
document language. To define how the interface elements behave, and to make them 
object-oriented, you associate them with a "code-behind" class written in C# (pronounced 
see-sharp), a language with a similar syntax to C++ that's used for writing Microsoft .NET 
programs. 

• To create this application, we'll use Microsoft Visual Studio 2010 Express, which is the 
free version of Microsoft Visual Studio 2010, a development environment that supports C#, 
XAML, Visual Basic .NET, and other languages. (If you have the full Visual Studio, you can 
also develop in that, of course.) 

• To get set up, download and install Microsoft Visual Studio 2010 Express from 
http://microsoft.com/express/downloads and the Kinect SDK Beta 2 from 
http://kinectforwindows.org . Download the 32-bit or 64-bit version of the SDK depending on 
your edition of Windows 7; if you're unsure, open the Start menu and right-click on 
Computer, click Properties, and check whether the System Type line says "64-bit." If you 
want to do voice-recognition applications, then there are a few additional components you 
also need to install, but for now this is all we need. 



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Kinect Hacking: Weather Map 



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Kinect Hacking: Weather Map 



Step 4 — Use it! Make a Kinect weather map. 



© Make Projects www.makeprojects.com Page 6 of 20 



Kinect Hacking: Weather Map 




• Here's an application that replaces 
the video background behind a 
subject with a weather map, the 
way TV meteorologists use green 
screens — except with Kinect, you 
don't need a green screen. You can 
easily adapt this technique to other 
backgrounds and uses. 

• First we need to start getting data 
out of Kinect. Plug Kinect's USB 
plug into your computer and its 
power plug to an outlet. If the SDK 
is installed properly, Kinect's LED 
indicator should blink, and a 
Windows pop-up may also indicate 
that the Kinect device is ready. 

• To verify communication to the PC, 
go to the Start menu under 
Microsoft Kinect 1.0 Beta2 SDK, 
and run the SkeletalViewer or 
ShapeGame samples. A zip file 
with source code for these samples 
can be found in the same location 
in the Start menu. 

• To create the project, launch your 
IDE (either Visual Studio 2010 
Express or Visual Studio 2010) and 
select File -» New -» Project, then 
choose the WPF Application 
project template under Visual C# -» 
Windows. (WPF, or Windows 
Presentation Foundation, is an 
interface framework that can 
encompass XAML elements with 
C# code-behind, as with our 
project.) Enter "KinectWeatherMap" 
for the project name, select a 
directory if you don't like the 
default one, then press OK. This 
creates a blank WPF application. 



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Kinect Hacking: Weather Map 



To tell your app to access the 
Kinect SDK, find the Solution 
Explorer (or select it from the View 
menu), right-click on References, 
and click Add Reference. Click the 
.NET tab in the popup, then find 
and select 

Microsoft. Research. Kinect and 
press OK. (To help find 
Microsoft. Research. Kinect, click 
the Component Name header to 
sort by name.) Now we're ready to 
write some code. 



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Kinect Hacking: Weather Map 



Step 5 



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• Double-click on MainWindow.xaml. This is auto-generated XAML code for the default first 
window that opens when you run the application. The file defines what visuals and controls 
are displayed in that window, and defines names for use in the code-behind class. The file 
already includes a window tag and a Grid tag, and we'll add 2 Image tags to define the 
frames that will hold the Kinect camera image and the background weather image. To do 
this, replace the contents of 'MainWindow.xaml with: 

• <Window x : Class="KinectWeatherMap . MainWindow" 
xmlns=" http: //schemas .microsoft . com/ 
winfx/ 2006 /xaml /presentation" 

xmlns :x=" http: //schemas .microsoft. com/ winf x/2006/xaml" 
xmlns : local="clr-namespace :KinectWeatherMap" Title="Kinect 
Weather Map" WindowState="Maximized"xGridxlocal :Gif Image 
x:Name="weather Image" /> <Image Name="kinectlmage" 
stretch="Unif orm"/x/Gridx/window> (Copy and paste this text, but see the 
image for formatting.) 

• The Gif image tag references our own control that supports animated GIFs like the ones 
we'll be pulling from the National Weather Service. You can find code for the Gif image 
class, along with all other code for this project, and updates for future releases of Kinect 
SDK, at http://makeprojects.eom/v/29 . This article steps through different versions of the 
code routines as we add functionality, so be sure to paste in the correct version for the 
step you're at. 

• Add the new Gif image class by right-clicking KinectWeatherMap in the Solution Explorer, 
then Add -> Class. Name it Giflmage.cs and then overwrite the file contents by pasting in 
the Giflmage.cs code from the URL above. 



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Kinect Hacking: Weather Map 



Step 6 



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Kinect Hacking: Weather Map 



oe KirsectWeatherMap -Microsoft Visual Studio 



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}; 
> 

void InitKinect(i.jnt:"-f? runtime} 
{ 

If [i-untiJi* ■■ null] 

i-eturn; 

runtine-InitiaLii:ei(RunTl(P*QpTi-QrT5.1)seColDr | 

RunfiiceSpticrj-.UieDepThAnidPlayerlfl'dex | 



To work with the C# class, the 
code-behind for the XAML, open 
the Solution Explorer panel in the 
IDE, then click the little triangle 
next to MainWindow.xaml and 
double-click on 

MainWindow.xaml.es. Now we see 
the code-behind file and can write 
some code to talk to Kinect. To tell 
the compiler where to find the class 
definitions used in the code, we 
declare: 

• using 

Microsoft .Re search. Kinect . Nui ; 

Below the using statements, 
inside the Mainwindow class 
definition but before its constructor 
routine, add the following fields to 
store the most recent depth image 
and a color offset map that 
translates between pixel positions 
in the I R camera's depth image and 
color camera pixel positions: 

• ImageFrame 
lastDepthFrame; int [ ] 
co lor Of f setMap; 

Inside the constructor, add the 
lines below, which call the 
initKinect method (which we'll 
add next) to initialize the first 
Kinect plugged in. With no Kinect 
connected, the program will just 
silently do nothing. 

• this. Loaded += (s, e) 

=> { InitKinect (Runtime . Kinect s . 
FirstOrDefault( ) ) ; } ; (See 
image for formatting) 

After the constructor in 
MainWindow.xaml.es add the 



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Kinect Hacking: Weather Map 



methods InitKinect, 

runtime_DepthFrameReady, 

runtime_VideoFrameReady, 

and 

runtime_SkeletonFrameReady, 
pasting the code in from 
http ://makeprojects . com/v/29 . 
InitKinect configures Kinect to 
send us data and set up a 
coiorof f setMap array for us to 
use later, and the other 3 are event 
handlers that are called whenever 
Kinect sees new depth, RGB, or 
skeleton data. 

• Now try running the application by 
pressing the F5 key or selecting 
Debug -> Start Debugging. You 
should see a window with the RGB 
video image streaming from Kinect. 
Hello, World! We're also saving the 
depth image in the 
lastDepthFrame field, for 
processing later. 



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Kinect Hacking: Weather Map 



Step 7 — Remove the background. 



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Kinect Hacking: Weather Map 



Depth pixel byteO 
* 




i r 



Depth pkdbvtel 

I 



15 14 13 12 11 10 9 



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Distancebwbyte PlayerindeK 



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Distancehigh byte 



• The depth image provides 2 values 
for each pixel: its distance from 
Kinect's camera plane (in meters), 
and the player index, indicating 
which player the pixel belongs to, if 
any. The player index ranges from 
to 6, with for no player 
(background or furniture), and 1-6 
based on who enters the scene. In 
this application, each of the 76,800 
pixels (320x240) in the depth 
image consists of 2 bytes that 
contain both the depth data and the 
player index. 

• To remove the background, we're 
going to do some image processing 
using the player index. We'll create 
a new image to represent the 
foreground, initially set it to 
transparent, and then iterate over 
each depth image pixel. If the 
player index is not zero, we'll copy 
the corresponding RBG image pixel 
to our foreground image. 

• Since we're using images from 
both the IR and color cameras, we 
also need to convert between the 2 
slightly different sets of 
coordinates using the 
colorOffsetMap array that we set 
up in the constructor. All of this 
happens in the 

runtime_VideoFrameReady 

method that we created earlier. 

• Copy the "Remove the 
Background" version of the code 
from http://makeprojects.eom/v/29 . 
and paste it into the project code. 

• We're only using the player index, 
but if you also wanted to retrieve 



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Kinect Hacking: Weather Map 



the depth data from the image, you 
could add the following line inside 
the method's inner for loop, after 
defining the depthindex variable: 

• short depth = (short) 
( (depthBytes [depthindex] 
» 3) | 

(depthBytes [depthindex + 
1] « 5) ); 



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Kinect Hacking: Weather Map 



Step 8 




Now compile and run the 
application. You should see a blank 
white background on your 
computer, until you or someone 
else moves into Kinect's field of 
view, at least from the waist up. 
When you do, the player index will 
become non-zero for pixels where 
Kinect is tracking your body, the 
code will copy over those color 
pixels, and you'll see an image with 
only people and no background — 
like a green screen without a green 
screen! 

You may notice that the "cutout" 
doesn't always match the RGB 
image, especially if you're moving 
quickly. This glitch is partly noise, 
partly because the RGB and depth 
frames may not be delivered at 
exactly the same rate, and partly 
because our code is simplified for 
learning, rather than optimized for 
speed. There are several 
techniques an intermediate 
developer could use to speed up 
the code and to sync the RGB and 
depth frames better, based on 
timestamp. 



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Kinect Hacking: Weather Map 



Step 9 — Track the skeleton and add the maps. 




• Finally, we want to add the weather 
maps in the background and be 
able to switch them using a simple 
gesture. To recognize the gesture, 
we'll use Kinect's skeleton tracking 
data. 

• What kind of gesture? Broadcast 
meteorologists often change the 
weather map as they walk across 
the screen and pivot to face the 
opposite direction. 

• To detect this gesture, we need to 
check 2 conditions: which side of 

the image the ShoulderCenter 

joint is on, and whether the left 
shoulder or right shoulder is closer 
to the camera. If both of these 
conditions change from their 
previous state, we know the user 
has performed the walk-and-turn 
gesture and we can cycle the 
background image. We check for 
turning so that the background 
doesn't cycle when the user is just 
reaching for the far side of the 
map. 

• To add this feature, we first need to 
add a few fields at the top of the 

MainWindow class: 

• int currentBackground = 
-If List<string> bglmages 
= new List<string> ( ) ; 
bool isPoseLeft = false; 
bool isPoseRight = 
false; 



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Kinect Hacking: Weather Map 



Step 10 



© Make Projects www.makeprojects.com Page 18 of 20 



Kinect Hacking: Weather Map 



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-r-iage, 

-ridge 

- ridge /i 
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ip.gLf"); 
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bgl mages. Add( "http://™! an. H?Bt her .gotf/l 
l -ridBe/CDnu£/H»p>H3tLoop_Ein3ll.gi-F->j 
bglmages.jld*! " titt p : ft rad iar .mat her. gov/ 1 
^ririie/Cflnus/LcM^soutSievisLJlarip . gif "); 
b£lm=ses.Adc("littp:;7rBd or. met her. gov/1 
— , rirlee/l.onus J 'Lcop J 'ncrtheai- , t_lor.p , eiF"): 
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— Tl.dtfi'/CiJlu.s/l (SOpVp* iWTIwstMirtp.glfl; 
hairf.ags5.jido( •Jittpi/yradaw .tuotEhsr-pH^l 
w ^idEe/con,i..■■Lc t -■p.■ , p3:scLlt(,.est_:c!)p,gi■l :, ■); 
LycleBac^roundO; 



• To retrieve the map images, add 
the following inside the 
MainWindow constructor after the 

Call to InitializeComponent ( ). 

You can substitute the URLs for 
other animated GIF maps provided 
by the National Weather Service: 

• bglmaaes . Add( " http: //radar .weather .gov/ 
ridge/Conus/Loop/NatLoop_Small 
•gif"); 

bglmages . Add( " http: //radar .weather .gov/ 

ridge/Conus/Loop/southeast_loo 

p. gif"); 

bglmages . Add ( " http: //radar .weather .gov/ 

r idge/Conus/ Loop/ nor theast_loo 

p. gif " ) ; 

bglmages .Add( " http: //radar .weather .gov/ 

r idge/Conus/ Loop /pacnorthwest_ 

loop. gif " ) ; 

bglmages . Add( " http: //radar .weather .gov/ 

r idge/Conus/ Loop /pacsouthwest_ 

loop. gif " ) ; 

CycleBackground( ) ; 

• Now update the 

runtime_SkeletonFrameReady 

method to the code version under 
"Track the Skeleton" at 
http ://makeprojects . com/v/29 . and 
also add the new 

CycleBackground( ) method, 

which cycles through the 
background images with each 
body-turn gesture. The code will 
find the skeleton closest to the 
Kinect and use shoulder positions 
to determine if the skeleton is 
facing right or left, and if the pose 
changes it will call 

CycleBackground to put up a 



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Kinect Hacking: Weather Map 



new animated background image, 
which is downloaded automatically. 

• Now stand up, and with your best 
voice, describe and gesticulate 
over the weather map background. 
To change images, walk to the 
other side of the image while 
turning your shoulders toward the 
center. 

• Congratulations, you've just made 
a Kinect hack! Now go show it off 
to your friends and see what else 
you can come up with. 



This project first appeared in MAKE Volume 29 . 



This document was last generated on 2012-11-01 12:22:00 AM. 



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Page 20 of 20